This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Raltegravir is the most recent FDA-approved HIV medication and must be dosed twice daily. However, a drug interaction with an older HIV agent, Atazanavir, may permit Raltegravir to dosed once daily.The objective of this study is to determine the pharmacokinetics and safety of Raltegravir doesd with Atazanavir in healthy adult volunteers. The study design is a randomized cross-over between one of two arms: Raltegravir dosed at a standard dose twice daily (arm A) or Raltegravir dosed once daily with a standard single daily dose of Atazanavir (arm B). Blood and urine concentrations will be used to model the pharmacokinetics of Raltegravir alone and in combination with Atazanavir. If the average minimum Raltegravir concentration in the once daily arm is at least 40% of the concentration in the standard arm, then the combination will be judged eligible for further clinical efficacy studies in HIV-infected patients.